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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: peterb on July 27, 2014, 05:41:26 am

Title: passed leak-down test, oil burning mystery
Post by: peterb on July 27, 2014, 05:41:26 am

I have a 1975 GMC with 350, auto trans. Have been burning oil. Blue puff at start-up but donut otherwise see smoke. Replaced valve stem seals. No change. Checked, some oil in plugs 1&3. Did cylinder leak test with mechanic. All cylinders ok. Checked (intake) valve seals again, looked fine. Didnpt check exhaust valve seals (though these were replaced 6 mo. ago along with intakes. Cannot figure source of blue cloud. If oil were leaking from gasket below say manifold wouldn;t truck be smoking all the time, not just blue puff at startup....thought it was rings but since leak test checks out fine....I'm puzzled.

Title: Re: passed leak-down test, oil burning mystery
Post by: Captkaos on August 17, 2014, 02:48:10 pm

generally this is from leaking valve seals...